1) Field of the Invention
The present invention relates to a method of producing low oxygen-content molybdenum (Mo) powders, and more particularly to a method producing low oxygen-content Mo powders by reducing molybdenum trioxide (MoO3) using calcium (Ca).
2) Background of Related Art
Molybdenum (Mo) is one of transition metals on the Periodic Table, and pure Mo represents a silver-white color and has a significant stiffness property. In addition, the pure Mo has remarkably high melting point (2896 K) and boiling point (4912 K).
Since molybdenum (Mo) represents superior physical, chemical, and mechanical characteristics, molybdenum (Mo) is used in various industrial fields. In particular, Mo is spotlighted as a high-temperature source material. In addition, since molybdenum (Mo) makes various effects even if only a small amount of molybdenum (Mo) is contained, molybdenum (Mo) has been used as a main source material of special steel.
However, since molybdenum (Mo) is metal representing a high melting point as described above, the molding and the processing for molybdenum (Mo) is difficult. Accordingly, a related product must be manufactured through a powder metallurgy scheme after forming molybdenum (Mo) powders.
According to the related art, the most general scheme to obtain molybdenum (Mo) is to perform two-step reduction processes with respect to molybdenum trioxide (MoO3) at a hydrogen atmosphere.
Meanwhile, another scheme is to obtain metal molybdenum (Mo) through the mixture of metal representing oxygen reduction reaction superior to that of molybdenum (Mo).
According to the related art subject to the reduction process at the hydrogen atmosphere, the high content of oxygen remains in the reduced molybdenum (Mo) powders. Since at least one metal is mixed for use when performing a reduction reaction using metal representing oxygen reduction reaction superior to that of molybdenum (Mo), contamination may be caused with high probability due to the metal, and the retrieving of molybdenum (Mo) is difficult.
Mainly, the reduction to metal molybdenum (Mo) from MoO3 is performed by removing oxygen. Accordingly, it is more advantageous that the lower content of oxygen is contained in the finally reduced metal (Mo).
In particular, since high-melting point metal including molybdenum (Mo) represents high affinity with oxygen and gas impurities, the high-melting metal may be easily contaminated by oxygen and gas impurities. In this case, the excessively high content of oxygen contained in the metal causes the fragility.
Further, in the case of powders, as the content of oxygen is lowered, the density of powers may be enhanced when the powders are sintered. Accordingly, the molybdenum (Mo) powders having the low content of oxygen have been demanded.
In addition, as the particle size of the powders of the metal molybdenum (Mo) is reduced, the reaction activity may be increased. Accordingly, conventionally, there is a limitation in obtaining low oxygen-content Mo powders having a sufficiently small size.
Following cited references are provided as related arts.    Paper 1: “The reduction behavior from MoO3 to MoO2 by the mixed gas of Ar+H2” (Journal of the Korean Institute of Resources Recycling No. 20, Vol. 4, pp. 71-77, 2011).    Paper 2: “Solid state metathesis synthesis of metal silicides; reactions of calcium and magnesium silicide with metal oxides” (Polyhedron No. 21, pp. 187-191, 2002).